In EP 1 156 242 B1, a sealing ring is disclosed, which is designed as a radial shaft sealing ring, and which is constructed from a ring-shaped metal supporting body and a sealing lip attached to it. The radial shaft sealing ring, in the installed position, has a shaft passing through it, where the sealing lip separates in a sealing manner a hydraulic side, particularly one that is under pressure, or an internal space or a housing internal space, from an atmospheric side or an external space. Moreover, the sealing lip is pressed by means of an annular helical spring on the shaft, and in addition, an additional sealing lip, oriented towards the atmospheric side, can further reduce the introduction of soiling material in the direction of the hydraulic side, and thus in the direction of the housing internal space. The sealing lip is formed substantially by two cylindrical surfaces of a cone frustum, where the first cylindrical surface of a cone frustum is oriented towards the atmospheric side or towards the external space, and the second cylindrical surface of a cone frustum is oriented towards the hydraulic side or the internal space. The first cylindrical surface of a cone frustum presents a kink, so that, in the uninstalled state of the sealing ring, an angle α of 35-65°, preferably 45-60° can be formed between the axial direction and the first cylindrical surface of a cone frustum, in the area of the contact surface of the sealing lip on the shaft. The angle β of the second cylindrical surface of a cone frustum with respect to the axial direction in the uninstalled state is 15-30°, preferably 17-22°. In the installed position of the sealing ring with the shaft, the angles α and β are approximately of equal size, and then have values between 20 and 50°, preferably 30°. This change of the angles α, β of the uninstalled state compared to the installed position is explained by an overlap, due to which, when the shaft is introduced into the sealing ring, on the one hand, precisely this change in angle occurs, and, on the other hand, the periphery of the sealing lip at the time of the installation of the shaft is elastically broadened.
In DE 24 58 773 A1, a seal is described, particularly for rotary shafts, which consists of a metal ring-shaped supporting body, to which a sealing lip is attached. To prevent buckling due to a pressure load caused by the pressure in the housing internal space, the surface which is oriented towards the external space and forms the sealing lip is designed so it is free of kinks. In addition, any discontinuities of precisely this surface, which delimits the sealing lip, and which is oriented towards the external space, would potentially lead to a folding over or folding down of the sealing lip, in the installation of the shaft. This effect can be decreased or prevented by a design without kink or a design without discontinuity. Here, the angle between this surface delimiting the sealing lip in the area of the contact surface of the sealing lip on the shaft—before the installation of the shaft—is at least 35°. Due to the overlap, this angle may end up being smaller in the installed position of the seal with the shaft. In addition, due to a potential relative excess pressure generated in the housing internal space, the value of this angle can be further decreased.
Sealing rings whose sealing lips are delimited by mutually intersecting tapered surfaces, that is cylindrical surfaces of a cone frustum, are thus usually used as seals in the area of housing openings, in which a shaft passes through the housing. Usually, the lip of the sealing ring, with respect to the surface to be sealed off or with respect to the shaft to be inserted in the sealing ring, presents a radial overlap, so that when the shaft is inserted into the sealing ring, the sealing lip is under radial preliminary tension and broadened. Due to the radial preliminary tension, the sealing lip encloses the surface or shaft to be sealed off in a sealing manner. In the case of large inner diameters >20 mm of the forming ring-shaped contact surface of the sealing lip on the shaft, the preset overlap of the sealing lip towards the shaft surface to be sealed off has nearly no effect on the axial width of the contact surface. This is due to the fact that sealing rings with large diameters and associated large sealing lip peripheral lengths, at the time of their installation on the shaft, can be broadened without problem by the amount of the overlap, without disadvantageous effect on the radial contact pressure of the sealing lip on the surface to be sealed off, and thus on the axial width of the contact surface. However, the smaller the shaft diameter, and thus also the inner diameter of the ring-shaped contact surfaces of the sealing rings, becomes, the smaller the resulting possible expansion of the sealing lip over the periphery is. Accordingly, with decreasing shaft radius or inner diameter of the contact surface of the sealing lip on the shaft, a broadening of precisely this contact surface can occur due to an undesired large deformation and contact pressure of the sealing lip on the surface to be sealed off. However, a broadening of the contact surface causes greater wear of the sealing lip as well as a worsened, undifferentiated sealing behavior. If, in addition, the contact surface is shifted more strongly towards the external space or towards the atmospheric side, particularly during start-stop operation, nicking or notching in the sealing lip occurs increasingly, particularly in the case of insufficient lubrication. As a result, leaks can develop in the area of the sealing lip.